1. Technical Field
The present invention relates to the cementitious encapsulation of waste material and/or contaminated soils containing heavy metals, to render them immobile, and particularly to the immobilization of heavy metals in such wastes and/or contaminated soils.
2. Description of the Prior Art
U.S. Pat. No. 3,841,102 teaches mixing waste material with an aqueous solution of an alkali metal silicate and a silicate setting agent. A preferred silicate setting agent is Portland cement. Portland cement is a calcined admixture of lime and clay, and contains basic calcium silicates, calcium aluminates, and calcium ferrites. The alkali metal silicate and silicate setting agent are reactive with each other and convert the admixture to a stable earth-like material. A leach test conducted on an admixture of waste material, alkali metal silicate, and silicate setting agent, wherein the waste material comprised heavy metals, produced a leachate having only small amounts of the heavy metals.
U.S. Pat. No. 3,980,558 discloses that processes using an alkali metal silicate and a silicate setting agent produce a highly porous solid having low compressive strength which is readily broken down to a dirt-like consistency from which toxic materials, such as arsenic, can be leached. In the '558 patent, an admixture is prepared which consists essentially of a liquid or semi-liquid waste having 30 to 40 percent by volume solids and a hydraulic cement. A type 1 Portland cement is preferred.
U.S. Pat. No. 4,142,912 discloses mixing arsenic, preferably in solid or slurry form, with a water-soluble alkaline earth metal salt or manganese salt, Portland cement, sand and water. The admixture sets to a rock-like substance which retains the arsenic component. Examples of water-soluble alkaline earth metal salts are calcium chloride, magnesium chloride, and magnesium sulfate. An example of a manganese salt is manganese chloride.
U.S. Pat. No. 4,149,968 discloses the treatment of an industrial waste containing metal ions. The waste is first treated with bentonite clay. The bentonite clay exhibits ion exchange properties in which the clay gives up sodium and potassium ions, and absorbs the metal ions. The admixture of industrial waste and bentonite clay is then mixed with Portland cement. The Portland cement, following setting, traps and binds the clay and contained waste materials.
U.S. Pat. No. 4,432,666 discloses preparing a cement binder, such as Portland cement, and a fine-grained waste which can include heavy metals, pouring the same into a container, and allowing the admixture to harden in the container.